Open Cloud Contextualization

Prepare the Virtual Machine Image

Step 1. Start a VM with the OS you want to Customize

Supported contextualization packages are available for the OS’s described in the platform notes.

Step 2. Download Contextualization Packages to the VM

RHEL 6.x (CentOS 6.x)


RHEL 7.x (CentOS/Oracle Linux 7.x)


RHEL 8.x (CentOS/AlmaLinux/Oracle Linux 8.x) and Fedora 29+




OpenSUSE 15 and Tumbleweed


ALT Linux p9, Sisyphus


Alpine Linux


FreeBSD 11, 12



Download the MSI package into C:\:

Or execute this command in powershell:

(New-Object Net.WebClient).DownloadFile("", "C:\one-context-6.0.0.msi")

Step 3. Install Contextualization Packages and Dependencies

RHEL 6.x (CentOS 6.x)

yum install -y epel-release
yum install -y one-context-[0-9]*el6*rpm

RHEL 7.x (CentOS/Oracle Linux 7.x)

yum install -y epel-release
yum install -y one-context-[0-9]*el7*rpm

RHEL 8.x (CentOS/AlmaLinux/Oracle Linux 8.x) and Fedora 29+

yum install -y epel-release
yum install -y one-context-[0-9]*el8*rpm
systemctl enable network.service


zypper --no-gpg-check install -y one-context-[0-9]*suse*rpm

ALT Linux

apt-get install -fy one-context-[0-9]*alt*rpm


apt-get purge -y cloud-init
dpkg -i one-context_*deb || apt-get install -fy

Alpine Linux

apk add --allow-untrusted one-context-[0-9]*apk


pkg install -y curl bash sudo base64 ruby open-vm-tools-nox11
pkg install -y one-context-[0-9]*.txz


Double-click on the downloaded MSI package icon in the same way you open other documents to install it.

Step 4. Run Sysprep in Windows Machines

Execute sysprep to prepare the OS for duplication. You can find more information at:

Step 5. Power Off the Machine and Save it

After these configuration is done you should power off the machine, so it is in a consistent state the next time it boots. Then you will have to save the image.

If you are using OpenNebula to prepare the image you can use the command onevm disk-saveas, for example, to save the first disk of a Virtual Machine called “centos-installation” into an image called “centos-contextualized” you can issue this command:

onevm disk-saveas centos-installation 0 centos-contextualized

Using sunstone web interface you can find the option in the Virtual Machine storage tab.

Set Up the Virtual Machine Template

The Virtual Machine Template has a section called context where you can automate different configuration aspects. The most common attributes are network configuration, user credentials and startup scripts. These parameters can be both added using the CLI to the template or using Sunstone Template wizard. Here is an example of the context section using the CLI:

    TOKEN = "YES",
    NETWORK = "YES",
    START_SCRIPT = "yum install -y ntpdate"

In the example we are telling OpenNebula to:

  • Set OneGate token and onegate information in the context
  • Add network configuration to the Virtual Machine
  • Enable login into the Virtual Machine using ssh with the value of the user’s parameter SSH_PUBLIC_KEY
  • On Virtual Machine boot execute the command yum install -y ntpdate

OneGate Token

OpenNebula has a centralized service to share data between Virtual Machines and the main daemon, useful to set monitoring information that can be gathered inside the VM and configuration data. It also lets you send scaling actions when the Virtual Machine belongs to a Service.

To do so the client installed with the contextualization packages (onegate) needs some information:

  • Token: it’s the key specific to each VM used to authenticate with the service
  • OneGate endpoint: the address where the OneGate daemon is reachable

To fill this information you have to specify TOKEN = "YES" in the contextualization section.

Network Configuration

OpenNebula does not rely on a DHCP server to configure networking in the Virtual Machines. To do this configuration it injects the network information in the contextualization section. This is done with option NETWORK = "YES". When OpenNebula finds this option it adds the IP information for each of the network interfaces configured plus extra information that resides in the Virtual Network template, like DNS, gateway and network mask.

The parameters used from the Virtual Network template are explained in the Managing Virtual Networks section.

User Credentials

One of the other very important things you have to configure is user credentials to connect to the newly created Virtual Machine. For linux base images we recommend to use SSH public key authentication and using it with OpenNebula is very convenient.

The first thing the users should do its to add their SSH public key (or keys) to its OpenNebula user configuration. This can be done in the Settings section of the web interface or using the command line interface:

oneuser update myusername
# an editor is opened, add this line

Then in the Virtual Machine Template we add the option:


Using this system the new Virtual Machines will be configured with the SSH public key of the user that instantiated it.

For Windows machines SSH is not available but you can use the options USERNAME and PASSWORD to create and set the password of an initial administrator.

    USERNAME = "Administrator",
    PASSWORD = "VeryComplexPassw0rd"


This password is encrypted in the virtual machine and in the virtual machine template.

Execute Scripts on Boot

To be able to execute commands on boot, for example, to install some software, you can use the option START_SCRIPT. When this option is used a new file that contains the value of the option will be created and executed.

For Windows machines this is a PowerShell script. For linux machines this can be any scripting language as long as it is installed in the base image and the proper shebang line is set (shell scripts don’t need shebang).

In this example some commands will be executed using bash shell that will install the package ntpdate and set the time.

    START_SCRIPT = "#!/bin/bash
yum update
yum install -y ntpdate

To add more complex scripts you can also use the option START_SCRIPT_BASE64. This option gets a base64 encoded string that will be decoded before writing the temporary script file.

Advanced Contextualization

There are more options that can be set in the contextualization section. You can read about them in the Virtual Machine Definition File reference section